According to Merriam-Webster, a clause is “a group of words containing a subject and a predicate and functioning as a member of a complex or compound sentence.” Clauses come in two pretty packages: the dependent and the independent.
An independent clause, or, “a group of words that contains a subject and predicate and expresses a complete thought,” is what is usually called a sentence. (We Grammarphiles say “independent clause” to be popular at parties.) This type of clause is the go-to car with a full gas tank; it can take you all the way to your destination.
A dependent clause is “a group of words that contains a subject and verb but does not express a complete thought.” Therefore, a dependent clause cannot be a sentence. This clause is…well, one of these. Don’t get the wrong idea: dependent clauses are not bad—they just cannot stand alone.
Why Writers Should Know This:
The only time an editor will pay attention to your dependent clauses is when you try to pass one off as a complete thought (read: sentence), like so:
When Jim was riding his bike.